Piezoelectric transducer mechanisms, such as bending transducers, may be used for generating electrical energy from mechanical deformations. In addition to a piezoelectric element, a bending transducer typically includes a support structure on which the piezoelectric element is fixedly attached. Via the support structure, a mechanical deformation may be introduced into the piezoelectric element, e.g., by vibrating the support structure. The support structure itself may be a second piezoelectric element. To pick off the voltage generated by the deformation of the piezoelectric element, electrodes, which in turn are contactable via contacting elements, may be provided on the piezoelectric element. Piezoelectric transducer mechanisms may be used in sensor and actuator technology in particular.
For example, German Patent Application No. DE 10 2005 062 872 A1 describes a device for detecting the rolling motion of a vehicle wheel in which a piezoelectric element is contacted on a chip carrier via the electrodes formed on its opposite sides, its upper electrode being contacted via a wire bond, and the chip carrier, including the piezoelectric element and the wire bond, are cast into a mold compound. In such sensors for measuring accelerations, e.g., vibrations, reliable contacting is possible with little complexity.
Moreover, piezoelectric materials are increasingly used for generating electrical energy from energies of the surroundings, in particular vibrations and deformations, which is also referred to as energy harvesting. Bending deformations of the piezoelectric element are enabled here which result in clearly higher energy generation than, for example, the mechanical strains of a piezoelectric element cast into a mold compound, as described in German Patent Application No. DE 10 2005 062 872 A1.
In bending transducers in which the support structure and the piezoelectric element are fixedly restrained, electrical contacting of the piezoelectric element may be implemented in a relatively simple manner since the piezoelectric element is fixedly connected to a housing. The use of a sufficiently large-surface and thus expensive piezoelectric element is generally required for such configurations. Furthermore, the areas of the piezoelectric element at the housing connection are particularly exposed to mechanical stresses which reduce the transducer's service life.
If the piezoelectric element is not fixedly restrained, contacting generally takes place via flexible wire connections. However, these wire connections are also exposed to the mechanical stresses that occur and have, with respect to the repeated deformations, only limited reliability.
German Patent Application No. DE 10 2007 006 994 A1 describes a circuit module, in particular for use in a vehicle tire, which has a bending transducer for generating electrical energy from mechanical deformations. The bending transducer contained in the circuit module includes an elastically deformable, vibration-capable support structure and a piezoelectric element. The support structure has a first restraining area and a second restraining area with which the support structure is mounted in a housing of the circuit module. The piezoelectric element is designed and situated on the support structure in such a way that a deformation of the support structure due to vibrations causes the piezoelectric element to be deformable. On its top and bottom sides, the piezoelectric element is coated by an electrically conducting layer which serves as lower and upper electrode, respectively. On the one hand, the support structure may be utilized for electrical contacting by designing it as a metallic spring device, in particular for contacting the lower electrode. On the other hand, the upper electrode formed on the upper side of the piezoelectric element may be contacted via additional contacting means such as a wire, a flexible printed circuit board, or a flexible metal sheet.